220 THE LAW. 



it is but a thing of yesterday; while to time geological we 

 turn as entering into every problem of our science, and in- 

 vesting their consideration with strange and deeper interest. 

 The amount of this time we have as yet no means of 

 estimating no power to give it expression in years and 

 centuries. Many ingenious calculations have, no doubt, 

 been made to approximate the dates of certain geological 

 events, but these, it must be confessed, are more amusing 

 than instructive. For example, so many lines of mud are 

 annually laid down by the inundation of the ISTile, frag- 

 ments of pottery have been found at the depth of thirty 

 feet. How many years have elapsed since the pottery was 

 first imbedded 1 Again, the ledges of Niagara are w r asting 

 at the rate of so many feet per century. How many years 

 must the river have taken to cut its way back from Queens- 

 town to the present Falls ? Again, lavas and melted basalts 

 cool, according to the size of the mass, at the rate of so 

 many degrees in a given time. How many millions of 

 years must have elapsed (supposing an original igneous con- 

 dition of the earth) before its crust had attained a state of 

 solidity 1 ? or, farther, before its surface had cooled down to 

 the present mean temperature? For these and similar com- 

 putations it will at once be perceived that we want the neces- 

 sary uniformity of factor ; and until we can bring elements 

 of calculation as exact as those of astronomy to bear on 

 geological chronology, it will be better to regard our " eras/' 

 and " epochs," and " cycles " as so many terms, indefinite 

 in their duration, but sufficient for the magnitude of the 

 operations embraced within their limits. Eut even on this 

 point of expressible time, the earnest geologist is not with- 

 out hope and encouragement. He rests confident (confi- 

 dent as in the existence of his own being) that the whole 

 history of geological phenomena the shifting of volcanic 

 energy from centre to centre, the elevation and depression 



